Epoxide with alkyne

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

By combining several click reactions, click chemistry allows for the rapid synthesis of useful new compounds of high complexity and combinatorial libraries. The 2-type reaction of the azide ion with a variety of epoxides to give azido alcohols has been exploited extensively in click chemistry. First of all, azido alcohols can be converted into amino alcohols upon reduction.70 On the other hand, aliphatic azides are quite stable toward a number of other standard organic synthesis conditions (orthogonality), but readily undergo 1,3-dipolar cycloaddition with alkynes. An example of the sequential reactions of... 

An alternative disconnection of homopropargylic alcohols substrates for intramolecular hydrosilylation is the opening of an epoxide with an alkynyl anion. This strategy was employed in a total synthesis of the macrolide RK-397 (Scheme 20). Epoxide ring opening serves to establish homopropargylic alcohol C with the appropriate stereochemistry. A hydrosilylation/oxidation protocol affords the diol E after liberation of the terminal alkyne. The... 

Styrenes [103], conjugated aT-dienes [107], and aT-enynes [108] are also epoxidized with ketones 57 in high ees (Table 5, entries 9-14). No isomerization of the epoxides was observed therefore only c/x-epoxides were obtained from cis-olefins. Alkenes and alkynes appear to be effective directing groups to favor the desired transition states T and V (Fig. 19). 

This benzene oxide may look very dubious and unstable, but benzene oxides can be made in the laboratory by ordinary chemical reactions (though not usually by the direct oxidation of benzene). We can instead start with a Diels-Alder reaction between butadiene and an alkyne. Epoxidation with a nucleophilic reagent (HO-O- from H2O2 and NaOH) occurs chemoselectively on the more electrophilic double bond—the one that is conjugated to the electron-withdrawing carbonyl group. 

The reductive cyclization of epoxides with alkenes and alkynes provides a very useful method for the synthesis of complex carbocyclic ring systems. Several interesting applications of this methodology have been reported in the past year. Two examples report the cyclization of an epoxide with an acrylate as the terminating group <07T 11341 ... 

During the first total synthesis of briarellin diterpenes, briarellins E and F, L.E. Overman and co-workers utilized the large reactivity difference between a triple and a double bond in peroxyacid oxidations to selectively epoxidize a trisubstituted double bond in the presence of a terminal alkyne." The epoxidation with mCPBA was carried out in DCM in the presence of a base to afford the a-epoxide in a 9 1 diastereomeric ratio. 

Alkynylation of Garner aldehyde F with alkyne E gave G with the required carbon skeleton. The triple bond of G was then reduced to give (Tf)-alkene H. The next epoxidation was unfortunately nonstereose-lective to give the required epoxide I and its isomer. Reduction of the epoxide I was fortunately selective with DIBAL-H as the reductant, and J was obtained after mesylation. 

Figure 7. Schematic representation of the modification of macroporous pHIPE by click reactions (1) formation of azide modified pHIPE by nuceophilic ring opening of epoxide groups on pGMA grafted pHIPE. (2) Click reactions with alkyne functional molecules. (Adapted from reference 31 by permission of The Royal Society of Chemistry.)...

Reaction medium. By virtue of its attributes supercritical carbon dioxide deserves its increasing applications as a reaction medium in synthesis. These include epoxidation" with oxygen and PhCHO, rhodium-catalyzed hydroboration, Pd(0)-catalyzed 1,4-hydroarylation of enones" and Heck reaction in the presence of Pd-C," carbonylation of aryl halides, Glaser coupling of 1-alkynes (mediated by CuCy using a solid ba.se (NaOAc)," as well as seandium(III) perfluorooctanesulfonate-catalyzed Diels-Alder and hetero-Diels-Alder reaetions. ... 

In contrast to the previous methods involving reductive coupling of two 71-components, a method involving participation of the sigma bond of an epoxide has been demonstrated. Treatment of a monosubstituted epoxide and alkyne with EtaB in the presence of a nickel catalyst generated from Ni(cod)2 and PBus affords homoallylic alcohols from reductive coupling (Scheme 3-67). The process proceeds with retention of epoxide stereochemistry, and intramolecular versions are endoselective. These aspects can be explained by initial oxidative addition of Ni(0) to... 

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